Cirrus Logic CS2200-CP - Manual (Page 13)

CS2200-CP
DS759F2 13
5.2.2 Ratio Modifier (R-Mod)
The Ratio Modifier is used to internally multiply/divide the R
UD
(the Ratio stored in the register space re-
mains unchanged). The available options for R
MOD
are summarized in Table 1 on page 13 .
The R-Mod value selected by RModSel[2:0] is always used in the calculation for the Effective Ratio
(R
EFF
), see “Effective Ratio (REFF)” on page 13 . If R-Mod is not desired, RModSel[2:0] should be left at
its default value of ‘000’, which corresponds to an R-Mod value of 1, thereby effectively disabling the ratio
modifier.
Table 1. Ratio Modifier
5.2.3 Effective Ratio (R
EFF
)
The Effective Ratio (R
EFF
) is an internal calculation comprised of R
UD
and the appropriate modifiers, as
previously described. R
EFF
is calculated as follows:
R
EFF
= R
UD
•
R
MOD
To simplify operation the device handles some of the ratio calculation functions automatically (such as
when the internal timing reference clock divider is set). For this reason, the Effective Ratio does not need
to be altered to account for internal dividers.
Ratio modifiers which would produce an overflow or truncation of R
EFF
should not be used; For example
if R
UD
is 1024 an R
MOD
of 8 would produce an R
EFF
value of 8192 which exceeds the 4096 limit of the
12.20 format. In all cases, the maximum and minimum allowable values for R
EFF
are dictated by the fre-
quency limits for both the input and output clocks as shown in the “AC Electrical Characteristics” on
page 7 .
RModSel[2:0] Ratio Modifier
000 1
001 2
010 4
011 8
100 0.5
101 0.25
110 0.125
111 0.0625
Referenced Control Register Location
Ratio...................................... “Ratio (Address 06h - 09h)” on page 21
RModSel[2:0] ........................ “R-Mod Selection (RModSel[2:0])” section on page 20